Tire manufacturers exercise the greatest care in constructing modem tires for a variety of vehicles. As the traveling speeds and distances traveled increase with more people on the roadways traveling at higher velocities and even greater distances than some years ago, tire manufacturers are assiduously working towards greater improvement in tire performance.
With the increased popularity of all terrain vehicles and the demands that owners make regarding performance of such vehicles, the need has arisen for greater safety and predictability with respect to tire characteristics.
As tire manufacturers strive to perfect their tires, they recognize the difficulty in achieving a tire with zero probability of error. Nevertheless, researchers and engineers work towards the development of an “intelligent tire” that will minimize the risk of a catastrophic failure.
Thus, efforts have taken the form of developing a tire that will enable the driver to recognize an impending tire failure from having fill information about the operating condition of the tire far enough in advance so that the vehicle can be brought to a standstill safely in a time span short of an accident.
As described in European Patent Application 849 597, a tire comprising at least one magnetized area can be used to provide information regarding the rotary speed of the tire when mounted on a vehicle. In addition, the tire may also provide information regarding the forces and/or torques acting on the tire, in particular, the circumferential torque, lateral force and radial force. We call this type of tire either an Intelligent® Tire or SWT® (Side Wall Torsion system) tire.
Usually, a magnetic field sensor(s) is mounted on the chassis of the vehicle. As the Intelligent® Tire rotates past the magnetic sensor(s) at a constant angular velocity, a magnetic field pattern or signature develops that is characteristic of the tire's materials, construction and deformation state. In particular, magnetic field amplitude signatures and phase signatures (difference in the alignment of two annular magnetic bands, one near the bead of the tire and the other near the tread) are found to be useful. For example, if the angular velocity of the tire changes, such as through a braking or acceleration maneuver, the magnetic field signature also changes, thus allowing for the measurement of circumferential torque acting on the tire using suitable algorithms. Furthermore, as described in U.S. patent application Ser. No. 09/307,605, when any deformation of the Intelligent® Tire occurs, such as through the application of a lateral force resulting from a cornering maneuver, there is an accompanying change in the magnetic field signature allowing for the measurement of the acting force using suitable algorithms. The information can be interfaced to vehicle control systems to improve, for example, antilock braking systems (ABS), traction control systems (TCS), rollover prevention systems (ROP) and electronic stability program (ESP) performance.
In the past, such monitoring activities generally used a passive integrated circuit embedded within the body of the tire and activated by a radio frequency transmission which energizes the circuit by inductive magnetic coupling. Passive devices which rely on inductive magnetic coupling or capacitive coupling generally have the disadvantage of requiring lengthy coil windings, thus requiring major modifications in the tire construction and assembly process. Another serious disadvantage with such passive devices is that an interrogator must be positioned in very close proximity to the tire, usually within a few inches of the tire, in order to allow communication between the tire and the device. Because of the proximity requirements, continuous monitoring is impractical since it would require that an interrogator be mounted at each wheel of the vehicle. Manual acquisition of data from the passive devices embedded in each of the tires of a parked vehicle is also cumbersome and time consuming because of the proximity requirements.
Another disadvantage with known tire monitoring and identification devices is that communication transmissions are achieved using conventional radio frequencies which generally require a relatively large antenna which must be mounted externally or secured to the tire in such a manner which requires relatively major modifications in the tire construction or assembly process.
Prior approaches to monitoring tire conditions and identification with various communication techniques have met with limited success. In one approach disclosed in U.S. Pat. No. 5,960,844, a method for monitoring tires included an activatable memory device permanently mounted within at least one tire of a vehicle on the inner surface. The device contained stored data pertaining to the tire, and in which the memory device was activated by means of a monitoring device mounted on the tire rim within the pressurized cavity formed within the tire.
In a different approach shown in U.S. Pat. No. 5,573,610, a method for monitoring various conditions of pneumatic tires and to tires containing a monitoring device involved monitoring tires which used an active, self-powered, programmable electronic device which was generally installed in or on the interior portion of a pneumatic tire or on a tire rim. The device could be used for monitoring, storing and telemetering information such as temperature, pressure, tire mileage and/or other operating conditions of a pneumatic tire along with tire identification information.
In yet another approach, U.S. Pat. No. 5,562,787, a method of monitoring tires was provided in which an activatable monitoring device was mounted within at least one tire of a vehicle, on the interior surface thereof, or on the tire rim. The device was activated by means of an interrogator signal having a frequency in the microwave range. In response to the signal, the monitoring device measured and transmitted information relating to one or more conditions such as the internal pressure and temperature of the tire, the number of rotations of the tire, and tire identification information. The monitoring device was secured within the tire in such a manner and location as to minimize stress, strain, cyclic fatigue, impact and vibration.
In still yet another approach, U.S. Pat. No. 5,573,611, the invention depicted was a method of monitoring tires which used an active, self-powered programmable electronic device which was installed in or on the interior surface of a pneumatic tire or on a tire rim. The device was activated by externally transmitted radio frequency waves and in response, the device compared or transmitted information and provided a warning in the event a preselected limit was exceeded. An interrogator was used to communicate with and retrieve digitally coded information from the electronic monitoring device.
In U.S. Pat. No. 5,838,229, a system for indicating low tire pressure in vehicles was depicted. Each vehicle wheel had a transmitter with a unique code. A central receiver in the vehicle was taught, at manufacture, to recognize the codes for the respective transmitters for the vehicle, and also a common transmitter code, in the event one of the transmitters needed to be replaced. During vehicle operation and maintenance, when the tires were rotated, the system could be recalibrated to relearn the locations of the transmitters.
In another application, U.S. Pat. No. 5,731,754, the invention included a transponder and sensor apparatus with on-board power supply mounted in or on a vehicle tire. A pressure sensor, a temperature sensor and a tire rotation sensor were mounted in a housing along with the transponder the power supply and an antenna. Upon receipt of an interrogation signal from a remote interrogator, the transponder activated the sensors to sense tire pressure and temperature and then backscatter-modulate the radio frequency signal from the interrogator with the tire condition parameter data from the sensors to return the backscatter modulated signal to the interrogator.
In yet another application, U.S. Pat. No. 5,977,870, a method for monitoring various engineering conditions of a pneumatic tire such as temperature, pressure, tire rotation and other operating conditions of the tire was depicted. A tire tag was mounted on the interior of the tire within the pressurizable cavity and contained the stored data and sensors for detecting certain conditions within the cavity. A separate transponder was mounted on the tire rim. The tire tag contained a battery, an antenna and stored data pertaining to the tire. The transponder used electronic circuitry for collecting data from the tire tag. The tire tag was actuated by transmitted radio frequency waves from the transponder, which data was transmitted by the transponder to the remote location by an antenna which extended from the transponder through the rim to a location externally of the tire.
In spite of the teachings of the above-mentioned patents, there is still a significant need for a tire monitoring system for sensing, transmitting, and interpreting the operating condition of the vehicular tire in advance of an impending failure. This information could be used to bring the vehicle to a standstill safely in a time span short of an accident.